1. Technical Field of the Invention
The present invention relates to a process for forming portions of a compound material inside a cavity of an integrated circuit device and to an electronic circuit incorporating portions of compound material thus obtained.
2. Description of Related Art
The increase in electrical performance and level of integration of electronic circuits requires the design and fabrication of circuits having complex geometrical configurations. As an example, some field-effect transistors or MOS (Metal Oxide Semiconductor) transistors have a gate which completely surrounds the channel of these transistors so as to obtain better control of the conduction state of the transistor. A conducting part of the gate must therefore be formed beneath the channel, that is to say between the channel and a subjacent substrate that supports the circuit. Such MOS transistors are known as GAA (Gate All Around) transistors.
It is possible to fabricate such GAA transistors by superposing portions of materials formed in succession from the surface of a substrate, as a stack of these portions. In this case, the lower part of the gate is firstly formed above the substrate using a conducting material, then the channel, generally based on silicon, is formed above this lower gate part, and the gate is completed by forming the upper gate part above the channel. Lateral parts of the gate may be formed at the same time as the lower part or as the upper part, but at least two steps for forming the various parts of the gate are needed, making the transistor fabrication process relatively long.
In general, producing a single conducting element in several separate steps gives rise to inhomogeneities within this element, even if the element consists of a single material used in each step of its production. Such inhomogeneities have an undesirable effect on the final electrical behavior of the element.
Moreover, it is known to produce portions of a metal-silicide-type material selectively in defined regions of an electronic circuit. To do this, silicon is initially placed in these regions and, at a stage in the circuit fabrication process in which these regions are exposed, the circuit is covered with a layer of a metal capable of forming a silicide-type compound. The circuit is then heated so as to form this silicide compound in the regions where the metal is in contact with the silicon. After the heating, the metal parts deposited outside the silicon regions therefore remain unaffected and are removed, for example by dissolving them in a suitable chemical solution. Since the silicide is insoluble in the solution used, it remains in the final circuit within the initial silicon regions.
This method of forming silicide portions has a drawback in that the silicon regions within which the silicide is formed must be initially exposed. This constraint may be incompatible with a complex configuration of the electronic circuit.
There is accordingly a need to overcome this drawback in the production of integrated circuit devices.